Sensing a property of a bladder wall

ABSTRACT

An apparatus for sensing a property of a bladder wall, such as bladder-wall oxygen, comprises an elongate catheter ( 1 ) and an elongate sensor ( 2 ). The catheter ( 1 ) defines a path from a proximal end of the catheter to a distal end of the catheter. The catheter comprises a sensor channel for guiding the elongate sensor along at least a part of the path, the sensor channel opening at a sensor port ( 3 ) towards the proximal end of the catheter. The sensor channel comprises (i) an enclosed lumen portion ( 10 ), arranged to surround the sensor, and (ii) an open furrow portion ( 16 ). The furrow is located nearer to the distal end of the catheter than is the enclosed lumen. The furrow is arranged to allow the sensor ( 2 ) to exit the enclosed lumen ( 10 ) in a direction substantially parallel to, or tangential to, the path of the catheter ( 1 ) at a proximal end of the furrow.

CROSS-REFERENCE

This application is a section 371 U.S. National phase ofPCT/GB2017/053316, filed Nov. 3, 2017 which claims priority from GreatBritain patent application no. 1618656.1, filed Nov. 4, 2016, both whichare incorporated by reference in its entirety.

FIELD OF INVENTION

This invention relates to the sensing of a property of a bladder wall,for example the sensing of bladder-wall oxygen.

BACKGROUND OF THE INVENTION

Tissue hypo-perfusion occurs when insufficient blood is reaching thebody tissue of a human or animal. It is a major pathophysiologicaldeterminant of mortality and morbidity in acutely ill patients and inhigh-risk patients undergoing surgery. Medical and surgical outcome hasbeen linked to the degree of tissue-oxygen debt. Insufficient oxygen canlead to failure of organs (e.g., lung, kidney, gut) necessitatingadmission to an intensive care unit for organ support. Complicationsrelated to tissue hypo-perfusion range from poor wound healing,secondary infection, inability to tolerate enteral feed, and gastricstress ulceration through to multiple organ failure and death.Uncomplicated survival is associated with prevention of, or rapidrestoration from, the tissue oxygen debt. Mortality rates are high andlong-term disability is common in survivors. Studies have shown howearly resuscitation of the circulation in these patients canconsiderably improve outcomes.

It has been proposed to monitor oxygen partial pressure in theepithelial layer of the bladder in order to provide a convenient andearly way of detecting if a patient is suffering from tissuehypo-perfusion.

Indwelling urinary catheters (also called Foley catheters) are wellknown instruments for draining urine from a bladder continuously. Humanor animal patients who are unwell or undergoing major surgery routinelyhave a bladder (Foley type) catheter inserted via the urethra, in orderto allow urine to be continuously drained from the bladder. A Foleycatheter is inserted through the urethra so that the distal end of thecatheter sits in the patient's bladder. A small balloon is inflated nearthe tip of the catheter, inside the bladder, to hold the catheter inplace. The catheter has a drainage lumen, along its length, for drainingurine, and a second lumen for inflating and deflating the balloon asrequired. An additional lumen is sometimes provided for irrigating thebladder.

U.S. Pat. No. 5,389,217 describes a modified Foley catheter in which anelongate oxygen sensor, having an oxygen-sensing element envelopedwithin an oxygen-permeable membrane, is completely accommodated within achannel of the catheter. When the apparatus is placed in the patient'sbladder, the distal end of the sensor passes through an open port, at ornear the distal termination of the catheter, and extends beyond the tipof the catheter. In a preferred embodiment, the terminal part of thechannel carrying the oxygen sensor is defined by a bend where it meetsthe port in the tip of the catheter. This is said to allow the sensor,which is flexible, to extend beyond the catheter at an angle, when itemerges from the port, allegedly facilitating placement of the sensortip in the epithelial wall of the bladder.

The present applicant believes, however, that such an arrangement doesnot significantly facilitate placement of the sensor tip in theepithelial wall, and that it is problematic since it is incompatiblewith certain desirable sensor types.

SUMMARY OF THE INVENTION

An apparatus for sensing a property of a bladder wall, such asbladder-wall oxygen is provided. The apparatus comprises an elongatecatheter (1) and an elongate sensor (2). The catheter (1) defines a pathfrom a proximal end of the catheter to a distal end of the catheter. Thecatheter comprises a sensor channel for guiding the elongate sensoralong at least a part of the path, the sensor channel opening at asensor port (3) towards the proximal end of the catheter. The sensorchannel comprises (i) an enclosed lumen portion (10), arranged tosurround the sensor, and (ii) an open furrow portion (16). The furrow islocated nearer to the distal end of the catheter than is the enclosedlumen. The furrow is arranged to allow the sensor (2) to exit theenclosed lumen (10) in a direction substantially parallel to, ortangential to, the path of the catheter (1) at a proximal end of thefurrow.

DESCRIPTION OF THE DRAWINGS

Certain preferred embodiments of the invention will now be described; byway of example only, with reference to the accompanying drawings, inwhich:

FIG. 1 is a side view of a catheter and oxygen sensor embodying theinvention;

FIG. 2 is a close-up side view, with hidden lines, of the distal end ofthe catheter and oxygen sensor;

FIG. 3 is a close-up perspective view of the distal end of the catheter;and

FIG. 4 is a median-plane cross-sectional diagram of the male pelvis,showing the catheter and oxygen sensor in place.

DETAILED DESCRIPTION OF THE INVENTION

The present invention seeks to provide a more versatile solution tosensing a property of a bladder wall, including (but not limited to)sending bladder-wall oxygen.

From a first aspect, the invention provides an apparatus for sensing aproperty of a bladder wall, comprising:

-   -   an elongate catheter; and    -   an elongate sensor,        wherein the catheter defines a path from a proximal end of the        catheter to a distal end of the catheter; and wherein the        catheter comprises a sensor channel for guiding the elongate        sensor along at least a part of said path, the sensor channel        opening at a sensor port towards the proximal end of the        catheter, wherein the sensor channel comprises (i) an enclosed        lumen portion, arranged to surround the sensor, and (ii) an open        furrow portion, wherein the furrow is located nearer to the        distal end of the catheter than is the enclosed lumen, and        wherein the furrow is arranged to allow the sensor to exit the        enclosed lumen in a direction substantially parallel to, or        tangential to, the path of the catheter at a proximal end of the        furrow.

The invention also encompasses methods of using such apparatus.

Thus, from a second aspect, the invention provides a method of operatinga catheter apparatus, the apparatus comprising:

-   -   an elongate catheter; and    -   an elongate sensor,        wherein the catheter defines a path from a proximal end of the        catheter to a distal end of the catheter, and wherein the        catheter comprises a sensor channel for guiding the elongate        sensor along at least a part of said path, the sensor channel        opening at a sensor port towards the proximal end of the        catheter, wherein the sensor channel comprises (i) an enclosed        lumen portion, configured to surround the sensor, and (ii) an        open furrow portion, wherein the furrow is located nearer to the        distal end of the catheter than is the enclosed lumen,        the method comprising moving the sensor within the lumen portion        so as to cause the sensor to exit the enclosed lumen into the        open furrow portion in a direction substantially parallel to, or        tangential to, the path of the catheter at a proximal end of the        furrow.

Thus it will be seen by those skilled in the art that, in accordancewith the invention, a furrow (or trough, or elongate depression) in thesurface of the catheter allows the sensor to emerge from the enclosedsensor lumen of the catheter in a substantially straight line, withoutforcing the sensor to bend sharply when it emerges. This arrangementnevertheless still allows the sensor to emerge proximal of the distalend of the catheter, rather than emerging from the tip of the catheter.This allows the tip of the catheter to be completely enclosed, with noopenings, which minimises discomfort to the patient during insertion ofthe catheter, and avoids an opening from being blocked by the wall ofthe bladder when the distal end of the catheter abuts the bladder wall.By enabling the sensor to pass along a relatively smooth path, withoutany abrupt bends, the catheter can be used with sensors that haverelatively inflexible tips, such as a fibre-optic sensor having a metalcage at its tip.

The property may be a property that is indicative of a haemodynamicstatus of the bladder or of the bladder wall. The property may bebladder-wall oxygen. The sensor may be a sensor that is suitable forsensing the haemodynamic status of the bladder or bladder wall. Thesensor may be a pH sensor, a NADH sensor, a pCO2 sensor, a laser Dopplerflowmetry (LDF) sensor, an oxygen haemoglobin sensor, or any otherrelevant sensor. In one preferred set of embodiments, the sensor is anoxygen sensor.

The sensor may comprise a tip and a cable. The tip may be elongate—e.g.,between 5 mm and 20 mm long. The cable may contain one or moreelectrical conductors and/or one or more optical fibres. The cablepreferably comprises an outer sleeve—e.g., of a plastics material. Thetip may be less flexible than the cable. The tip is preferablyoxygen-sensing and preferably comprises a material which is reactive tooxygen—preferably a luminescent sensor material. For example, the tipmay comprise a platinum-complex-based oxygen-sensitive indicator dye,such as platinum octaethylporphyrin. In some embodiments, the tipcomprises an outer metal cage or shield; this can help to protect theoxygen-sensitive material from damage. The sensor may be partially orsubstantially as described in WO 2006/095191, by the present applicant,the entire contents of which are hereby incorporated by reference.

The open furrow preferably comprises a concave depression in an outerwall of the catheter. The furrow is preferably elongate along the pathof the catheter. The furrow may have any depth, but preferably has adepth—which may be a maximum depth, or which may be a mean depthmeasured along a deepest part of the furrow in the direction of the pathof the catheter—that is less than half the thickness of the catheteradjacent the furrow. This depth may be measured relative to a lateralline spanning left and right side walls or surfaces of the furrow, ormay be measured relative to the catheter—e.g., adjacent to the furrow inthe proximal or distal direction. The depth of the furrow is preferablymore than the mean or maximum thickness of the tip of the sensor, and/orof the cable of the sensor adjacent the tip, and/or of a mean or maximuminternal diameter of the enclosed sensor lumen. However, the depth ofthe furrow is preferably no more than twice or three times the mean ormaximum thickness of the tip of the sensor, and/or of the cable of thesensor adjacent the tip, and/or of a mean or maximum internal diameterof the enclosed sensor lumen. In this way, any bending of the sensor asit leaves the furrow can be minimised. The enclosed lumen portionpreferably opens into the furrow at a proximal end of the furrow,preferably wholly within the depth of the furrow—e.g., through anorifice in a proximal end surface of the furrow.

A base of the furrow is preferably at least as long as a tip, or otherrelatively-inflexible portion, of the sensor—e.g., at least 10 mm, 15 mmor 20 mm long. In this way, the tip can be accommodated fully within thefurrow, before being guided gently away from the catheter by a distalend surface of the furrow. The base may be a surface (e.g., a plane orsemicylinder), or it may be a line defined in part by the interface oftwo angled side walls. The furrow could possibly have alaterally-oriented, planar end wall (i.e., perpendicular to the path ofthe catheter); however, preferably the furrow comprises an inclineddistal end surface, which is preferably angled at more than 90 or 120degrees from a base of the furrow (or from the path of the catheter),but preferably less than 180 degrees—for example, more than 135 or 150degrees, and preferably less than 175 or 170 degrees. In a preferredembodiment, the end surface is inclined at 160 degrees. In this way, thedistal end face of the furrow will act to direct the tip of the sensorgently out of the furrow, as the sensor is pushed along the sensorchannel, even when the tip of the sensor is relatively inflexible orrigid. The distal end surface may be planar or curved. It may becontinuous with one or more side walls, or may join a side wall along anangled edge. If the distal end surface is curved, then a planetangential to the surface is preferably angled as described above.

Methods of operating the apparatus may comprise pushing the sensor alongthe sensor channel, such that a distal end face of the furrow directsthe tip of the sensor out of the furrow.

The inner face of the enclosed sensor lumen is preferably lined orcoated with a layer that has a lower coefficient of friction than thatof the material that defines the sensor lumen (i.e., than the materialthat is being lined or coated, which may be silicone in someembodiments). The layer may comprise fluorinated ethylene propylene(FEP) or polytetrafluoroethylene (PTFE) or a perfluoroalkoxy alkane(PFA). This has been found to greatly facilitate placement of thesensor, by allowing it to move easily within the catheter. The layer maybe bonded to the walls of the sensor lumen, or may simple sit withinit—e.g., as a co-extruded tube within the sensor lumen.

The catheter preferably comprises a urinary drainage lumen connecting adrain hole, located towards the distal end of the catheter, and adrainage port, located towards the proximal end of the catheter. Beinglocated towards the proximal end of the catheter may here mean anywherebetween a mid-point of the catheter, or a point on the catheter thattypically lies outside the patient's body, and the proximal end of thecatheter. In particular, if the catheter comprises a transparent tubeportion, as described below, the drainage port may be situated adjacentthe distal end of the transparent tube—i.e., near where the transparenttube joins a main body of the catheter—rather than being adjacent thesensor port at the proximal end of the transparent tube.

The catheter is preferably an indwelling urinary catheter, or Foleycatheter. The catheter may be made primarily (e.g., at least half bymass) of silicone. The drainage lumen and the sensor channel may beseparate, or they may comprise a common channel or lumen for at least apart of the respective lengths.

The sensor port is preferably located on the path, or axis, of thecatheter. By contrast, other ports, such as a drainage port and/orinflation port and/or irrigation port, may be displaced sideways from,and/or be at an angle to, the path of the catheter. This allows thesensor to enter the enclosed lumen, through the sensor port, on a“straight-through” path, with minimal or no bending. This reducesfriction between the sensor and the catheter.

The sensor port preferably comprises a fastener or securing means forresisting or preventing movement of the sensor relative to the sensorchannel. The fastener or securing means is preferably releasable. It maycomprise a clamp or seal. It may additionally act to prevent fluidescaping around the outside of the sensor. The sensor port preferablycomprises means for loosening the fastener or securing means, to allowthe sensor to be moved freely within the catheter when required. Thesensor port may, for instance, comprise a compressible annularbung—e.g., made of silicone—and a compression mechanism—e.g., a threadedplug. This may be used to compress the bung against the sensor, therebyincreasing friction on the sensor, to resist movement, and effecting aseal around the sensor.

The catheter preferably comprises an inflatable balloon located towardsthe distal end of the catheter (e.g., within 1 to 10 cm of the distalend). The catheter preferably also comprises an inflation lumen,connecting to the inflatable balloon. An inflation port may be locatedtowards the proximal end of the catheter. The drainage port andinflation port may be located adjacent each other in a connectingportion of the catheter. The balloon may have any appropriate size orshape, for retaining the catheter in a bladder of a patient, as is knownin the art.

The catheter may additionally comprise an irrigation lumen.

One or both of the sensor and the catheter preferably comprises adisplacement indicator or scale, for measuring or indicatingdisplacement of the sensor relative to the catheter. The displacementindicator may be marked on a transparent window of the catheter, or itmay be marked on an outer face of the sensor. It may comprise a distancescale having a plurality of regularly-spaced marks, or it may compriseone or more marks that indicate one or more significant relativepositions (e.g., when the sensor tip is aligned with a distal mouth ofthe enclosed sensor lumen). In a preferred set of embodiments, thecatheter comprises a transparent tube, through which the sensor maypass. The transparent tube may define the path of the catheter, over thelength of the tube. There is preferably a plurality of regularly-spacedmarkings on the tube—e.g., ten marks at one-centimetre intervals. Thesensor may comprise one or more marks on an outer face which cooperatewith the displacement indicator or distance scale to allow the positionof the sensor to be determined relative to the catheter. Thedisplacement indicator or scale may be such that it can be determinedwhen the distal tip of the sensor is located in, or near, the furrow.Preferably, the displacement indicator comprises one or more marks thatindicate when the sensor, or more particularly the distal tip of thesensor, is wholly within the enclosed sensor lumen—this can help toprevent injuring the patient during insertion and withdrawal of thecatheter. Preferably, the displacement indicator comprises one or moremarks that indicate when a tip of the sensor is located wholly beyondthe distal end or tip of the catheter—this can help prevent takingerroneous readings when the sensor tip is still touching the catheter.More generally, the displacement indicator or scale can aid accuratedeployment of the sensor, by saving the operator from having to rely onfeel alone, which may be unreliable if there is resistance to thepassage of the sensor through the enclosed sensor lumen. The distal endof the transparent tube is preferably joined to the rest of the catheter(referred to herein as the main body of the catheter) by a Luer lock.This can prevent any urine from leaking out of the catheter. The sensorport may be at the proximal end of the transparent tube.

The apparatus is preferably suitable for measuring or monitoring theproperty of the bladder wall, e.g., bladder-wall oxygen, qualitativelyand/or quantitatively. An external monitoring system may be connected tothe sensor port. Once the sensor is positioned against the bladder wall,the external monitoring system may take measurements of the propertycontinuously or at intervals. In one set of embodiments, the externalmonitoring system may take measurements of dissolved oxygen levels frombladder wall tissue—e.g., in units of kPa or mmHg—continuously or atintervals. The apparatus may thus comprise a monitoring system orcontrol unit, connected to the sensor, for measuring or monitoring thebladder-wall property (e.g., bladder-wall oxygen) in a human or animalpatient.

Methods of operating the apparatus may comprise inserting the elongatecatheter into a patient, preferably via the urethra, and preferably soas to locate a proximal end of the catheter in a bladder of the patient.Embodiments may comprise moving the sensor along the enclosed lumen toposition the tip of the sensor against a bladder wall of a patient. Theymay comprise using the sensor to measure or monitor the bladder-wallproperty for a patient. They may comprise the sensor being an oxygensensor and using the oxygen sensor to measure or monitor bladder-walloxygen for a patient.

FIG. 1 shows a Foley catheter 1 carrying an elongate oxygen sensor 2. Inother embodiments, different types of sensor may be used. FIGS. 2 and 3show close-ups of the distal end region of the catheter 1.

The main body of the catheter 1 is approximately 40 cm long and isformed from silicone. It comprises a relatively-rigid, proximalconnecting portion 6, or port hub, and a relatively-flexible,cylindrical, elongate portion 7. A smooth, domed tip 8 is bonded to thedistal end of the elongate portion 7.

The elongate portion 7 of the catheter 1 defines three lumens, runningside-by-side from the connecting portion 6 to near the tip 8 of thecatheter 1: an inflation lumen, a drain lumen 11, and a sensor lumen 10.The inflation lumen runs from an inflation port 12 in the connectingportion 6 to an inflatable balloon 13 which surrounds the elongateportion 7 and which is located around 5 cm proximal of the tip 8. Thedrain lumen 11 runs from a drainage port 14 in the connecting portion 6and terminates near the tip 8. The drain lumen 11 opens through a set ofsix drain holes 15 located along the elongate portion 7 of the catheter1, just proximal of the tip 8—three holes on each side of the catheter1. The sensor lumen 10 runs from a sensor port 3 towards the tip of thecatheter 1. The inside of the sensor lumen 10 is lined with fluorinatedethylene propylene (FEP).

The following steps may be taken during manufacture of the catheter 1:

-   -   the main body of the catheter 1 is extruded in long lengths        (typically several hundred meters) and comprises a        relatively-flexible, cylindrical, elongate; silicone structure,        over-molded over an FEP tube, to provide a sensor lumen 10, as        well as a cavity drain lumen 11 and another cavity inflation        lumen;    -   the main body extrusion is cut into lengths of approximately 34        cm;    -   approximately 2 cm of silicone is removed from a proximal end,        resulting in approximately 2 cm of FEP tube projecting from the        main body extrusion;    -   the proximal end of the main body extrusion, containing the        protruding 2 cm of FEP tube, is loaded into a mold tool, and the        connecting portion 6 is produced by over-molding silicone onto        the main body of the catheter 1;    -   the distal end of main body extrusion 1 is loaded into a        punching tool, and an aperture is produced which intersects the        inflation lumen, approximately 1 cm from the distal end;    -   the distal end of main body extrusion 1, containing the        inflation aperture, is loaded into a mold tool which over-molds        a silicone portion comprising drainage holes 15 connected to the        drainage lumen 11, as well as an open furrow 16 connected to the        sensor lumen 10; and    -   a smooth, domed tip 8 (molded separately in silicone) is bonded        to the distal end of the silicone portion, beyond the drainage        holes 15 and open furrow 16.

FIG. 1 shows the oxygen sensor 2 entering the catheter 1 through asensor port 3. The sensor port 3 contains a locking silicone bung, toprovide a seal around the outside of the sensor 2. The oxygen sensor 2then passes through a flexible transparent tube 4, along which is markeda distance scale 5. The transparent tube 4 is sealed to the connectingportion 6 by means of a Luer lock 9. The oxygen sensor 2 passes from thetransparent tube 4 into the sensor lumen 10 within the body of thecatheter 1.

The inflation port 12 and drainage port 14 are displaced a little to theside of the path of the elongate portion 7 of the catheter 1. However,the sensor port 3 lies on the path of the catheter 1. This reducesresistance to movement of the oxygen sensor 2.

The distal end of the enclosed sensor lumen 10 opens into an open furrow16, at a circular or oval mouth 23, approximately 3 cm before the tip 8.The furrow 16 runs for approximately 15 mm towards the tip 8, and isdefined by an elongate, concave depression in the outer walls of thecatheter 1. This can be seen particularly clearly in the close-up viewsof FIGS. 2 and 3. The furrow 16 is approximately 3 mm wide andapproximately 2 mm deep when measured against the cylindrical shape ofthe elongate portion 7. The sensor lumen 10 opens into the furrow 16 atone end, within the depth of the furrow 16. The furrow 16 is sized toaccommodate the oxygen sensor 2 within its depth. The side walls of thefurrow 16 slope approximately radially along the cylindrical shape ofthe elongate portion 7 of the catheter 1. The furrow 16 has a planar orcurved base 22, approximately 13 mm long and approximately 1 mm wide.The distal end wall 17 of the furrow 16 slopes at an angle ofapproximately 160 degrees to the base 22.

The elongate oxygen sensor 2 comprises a flexible, plastic-coated outersleeve which runs between a plug 19, at a proximal end of the sensor 2,to a sensor tip 18 at a distal end of the sensor 2. The sleeve containsan optical fibre. The plug 19 contains optical and electricalconnections, and associated electronic circuitry, for plugging thesensor 2 into a control unit (not shown). The sensor tip 18 isapproximately 10 mm long, and contains an oxygen-sensitive luminescentmaterial, such as platinum octaethylporphyrin, contained inside a rigid,elongate, perforated metal cage—for example, in an arrangementsubstantially as described in WO 2006/095191.

FIG. 4 shows the catheter 1 inside a human male. In use, aurine-collection vessel (not shown) is coupled to the drainage port 14,and the catheter 1 is inserted along the urethra 20 until its tip 8 islocated inside the bladder 21. The inflation port 12 is then used toinflate the balloon 13, in order to prevent the catheter 1 from beingprematurely pulled out of the bladder 21.

The oxygen sensor 2 may initially be separate from the catheter 1, ormay be located partially within the sensor lumen 10. The sensor port 3is loosened, and the oxygen sensor 2 is pushed along the sensor lumen10. The position of a reference mark (not shown) on the outside of theoxygen sensor 2 may be tracked against the distance scale 5 to determinethe location of the oxygen sensor 2 relative to the catheter tip 8.

It will be seen from FIG. 4 that the path of the urethra 20 is far fromstraight, typically containing at least two significant bends.Nevertheless, the FEP-lining of the sensor lumen 10 ensures that theoxygen sensor 2 can easily be moved backwards and forwards, by hand,within the sensor lumen 10.

After the sensor tip 18 reaches the distal end of the enclosed sensorlumen 10, it emerges from the mouth 23 into the furrow 16. The furrow 16is large enough to fully accommodate the rigid sensor tip 18. Unless alateral force is causing the end region of the catheter 1 to bendsignificantly, with further pushing of the oxygen sensor 2, the sensortip 18 will be deflected gently away from the catheter 1 as it meets andis guided outwardly by the sloping distal end wall 17 of the furrow 16.Further insertion of the oxygen sensor 2 will cause the sensor tip 18 toadvance past the tip 8 of the catheter 1, in substantially the samedirection as the end region of the catheter 1. The flexible nature ofthe cable portion of the oxygen sensor 2 allows an oxygen-sensing sidewall of the sensor tip 18 to come to rest against the wall of thebladder 21, in front of the catheter 1.

Once the catheter 1 and oxygen sensor 2 have been correctly placed, thesensor port 3 may be screwed tight in order to clamp the silicone bungaround the sensor sleeve 2, so as to prevent any movement of the oxygensensor 2 within the sensor lumen 10. The bung also prevents urinetravelling along the sensor lumen 10 and leaking out of the sensor port3.

The plug 19 of the oxygen sensor 2 can then be connected to a controlunit (not shown), which performs measurements of the oxygen partialpressure in the wall of the bladder 21. The control unit may control thesensor tip 18 substantially as described in WO2012/010884, by thepresent applicant, the entire contents of which are hereby incorporatedby reference.

It will be appreciated by those skilled in the art that the inventionhas been illustrated by describing one or more specific embodimentsthereof, but is not limited to these embodiments; many variations andmodifications are possible, within the scope of the accompanying claims.For example, other types of sensor may be used, including other types ofoxygen sensor; the catheter 1 may contain additional lumens, such as anirrigation lumen; one of the lumens may be contained inside another ofthe lumens; the catheter 1 may be made of a material other thansilicone; etc.

1. An apparatus for sensing a property of a bladder wall, comprising: anelongate catheter; and an elongate sensor, wherein the catheter definesa path from a proximal end of the catheter to a distal end of thecatheter, and wherein the catheter comprises a sensor channel forguiding the elongate sensor along at least a part of said path, thesensor channel opening at a sensor port towards the proximal end of thecatheter, wherein the sensor channel comprises (i) an enclosed lumenportion, arranged to surround the sensor, and (ii) an open furrowportion, wherein the furrow is located nearer to the distal end of thecatheter than is the enclosed lumen, and wherein the furrow is arrangedto allow the sensor to exit the enclosed lumen in a directionsubstantially parallel to, or tangential to, the path of the catheter ata proximal end of the furrow.
 2. The apparatus of claim 1, wherein theproperty is indicative of a haemodynamic status of the bladder orbladder wall.
 3. The apparatus of claim 1, wherein the sensor is a pHsensor, an NADH sensor, a pCO2 sensor, a laser Doppler flowmetry (LDF)sensor, or an oxygen haemoglobin sensor.
 4. The apparatus of claim 1,wherein the sensor is an oxygen sensor, and wherein the apparatus is forsensing bladder-wall oxygen.
 5. The apparatus of claim 1, wherein thefurrow is configured to allow the sensor to exit the enclosed lumen in adirection substantially parallel to, or tangential to, the path of thecatheter at a proximal end of the furrow as the sensor is moved alongthe sensor channel.
 6. The apparatus of claim 1, wherein the sensorcomprises a cable and a tip, wherein the tip of the sensor can beaccommodated wholly within the enclosed lumen portion and wherein thetip is less flexible than the cable.
 7. (canceled)
 8. (canceled) 9.(canceled)
 10. (canceled)
 11. (canceled)
 12. (canceled)
 13. (canceled)14. The apparatus of claim 1, wherein the open furrow comprises aconcave depression in an outer wall of the catheter, elongate along thepath of the catheter.
 15. The apparatus of claim 1, wherein the openfurrow has a depth that is between one and two times a maximum thicknessof a cable or a tip of the sensor.
 16. The apparatus of claim 1, whereinthe enclosed lumen portion opens into the furrow at a proximal end ofthe furrow, wholly within the depth of the furrow.
 17. The apparatus ofclaim 1, wherein the furrow has a base that is at least as long as anelongate tip of the sensor.
 18. The apparatus of claim 1, wherein thefurrow has a distal end wall that is angled at between 120 and 170degrees from a base of the furrow, so as to direct a tip of the sensorout of the furrow as the sensor is moved along the sensor channel. 19.(canceled)
 20. The apparatus of claim 1, wherein an inner face of theenclosed sensor lumen is lined or coated with a layer that has a lowercoefficient of friction than the coefficient of friction of a materialthat defines the sensor lumen.
 21. (canceled)
 22. The apparatus of claim1, wherein the sensor port comprises a compressible annular bung forresisting movement of the sensor relative to the sensor channel. 23.(canceled)
 24. The apparatus of claim 1, wherein one or both of thesensor and the catheter comprises a displacement indicator, forindicating displacement of the sensor relative to the catheter andwherein the displacement indicator comprises one or more marks thatindicate when a distal tip of the sensor is wholly within the enclosedsensor lumen or that indicate when a tip of the sensor is located whollybeyond the distal end of the catheter.
 25. (canceled)
 26. (canceled) 27.(canceled)
 28. (canceled)
 29. A method of operating a catheterapparatus, the apparatus comprising: an elongate catheter; and anelongate sensor, wherein the catheter defines a path from a proximal endof the catheter to a distal end of the catheter, and wherein thecatheter comprises a sensor channel for guiding the elongate sensoralong at least a part of said path, the sensor channel opening at asensor port towards the proximal end of the catheter, wherein the sensorchannel comprises (i) an enclosed lumen portion, configured to surroundthe sensor, and (ii) an open furrow portion, wherein the furrow islocated nearer to the distal end of the catheter than is the enclosedlumen, the method comprising moving the sensor within the lumen portionso as to cause the sensor to exit the enclosed lumen into the openfurrow portion in a direction substantially parallel to, or tangentialto, the path of the catheter at a proximal end of the furrow.
 30. Themethod of claim 29, wherein the furrow has a distal end face and whereinthe method further comprises pushing the sensor along the sensor channelsuch that the distal end face of the furrow directs a tip of the sensorout of the furrow.
 31. The method of claim 29, further comprisinginserting the catheter into a patient, via the urethra, so as to locatea proximal end of the catheter in a bladder of the patient.
 32. Themethod of claim 29, further comprising moving the sensor along theenclosed lumen to position a tip of the sensor against a bladder wall ofa patient.
 33. (canceled)
 34. The method of claim 29, further comprisingusing the sensor to measure a haemodynamic status of the bladder orbladder wall of a patient.
 35. The method of claim 29, wherein thesensor is an oxygen sensor and the catheter apparatus is anoxygen-sensing catheter apparatus; the method further comprising usingthe oxygen sensor to measure bladder-wall oxygen for a patient. 36.(canceled)